Presence Of Mixture Research Articles

Oxidation of phenyl alanine by pyridinium chlorochromate in acidic DMF–water medium: A kinetic study

The kinetics of oxidation of phenyl alanine by pyridinium chlorochromate in DMF–water (70:30%) mixture in presence of perchloric acid leads to the formation of corresponding aldehyde. The reaction is of first order each in [PCC], [HClO4] and [AA]. Michaelis–Menten type kinetics was observed with phenyl alanine. The reaction rates were determined at different temperatures [25, 30, 35, 40, 45, 50°C] and the activation parameters were calculated. The reaction does not induce polymerization of acrylonitrile. With an increase in the amount of DMF in its aqueous mixture, the rate increases. A suitable mechanism for the reaction was postulated.

A study of bioflotation of chalcopyrite and pyrrhotite mixtures in presence of L. ferrooxidans

The objective of this work was to determine the behaviour of chalcopyrite (Cp) and pyrrhotite (Po) in microflotation tests using pure minerals and mixtures in the presence of Leptospirillum ferrooxidans. Tests were carried out in the presence and absence of an unconventional collector, isopropyl ethyl thionocarbamate. The results indicate that chalcopyrite and pyrrhotite act differently alone than in a mixture which means the presence of pyrrhotite inhibits chalcopyrite recovery. For chalcopyrite, the flotation rate significantly increases in the presence of bacteria in the first 10 min of contact which is an indication of a first order kinetic equation. The results in the presence of an unconventional collector suggest that the interaction between mineral and thionocarbamate is chemical and not due to the galvanic effect.L’objectif de ce travail consistait à déterminer le comportement de la chalcopyrite (Cp) et de la pyrrhotite (Po) dans des essais de microflottation utilisant des minéraux purs et des mélanges, en présence de L. ferrooxidans. Les essais étaient effectués en présence et en absence d’un collecteur non conventionnel, l’isopropyle éthyle thionocarbamate. Les résultats indiquent que la chalcopyrite et la pyrrhotite agissent différemment seuls que lorsque dans un mélange, ce qui signifie que la présence de pyrrhotite inhibe la récupération de la chalcopyrite. Pour la chalcopyrite, la vitesse de flottation augmente significativement en présence de bactéries dans le premier 10 minutes de contact, ce qui est une indication d’une équation cinétique de premier ordre. Les résultats en présence d’un collecteur non conventionnel suggèrent que l’interaction entre le minéral et le thionocarbamate est chimique et n’est pas due à l’effet galvanique.

Polyacrylic acid polymer modulates the UCST-type phase behavior of ionic liquid and water

Upper critical solution temperature (UCST)-type phase behavior was observed in the critical mixture of water (W) and hydrophobic ionic liquid, 1-hexyl-3-methylimidazolium tetrafluoroborate (IL), by refractive index and fluorescence measurements. The phase separation temperature depends on the composition of IL as well as water. Furthermore, for the first time, the behavior of high molecular weight polymer polyacrylic acid, PAA (Mw = 450 000 g mol−1), as an impurity in the UCST mixture was investigated by simultaneous refractive index (n) measurements for both the coexisting phases of ILW. The refractive index in each phase of ILW as well as three different PAA concentrations (C = 0.5, 1.0, and 1.5 mg cm−3) in the near critical composition of ILW have been measured at temperatures below the system's upper critical point. We observed that the polymer significantly affected on the critical region of ILW. The phase-transition region of coexisting phases of ILW significantly shifts down with an increase in the concentrations of PAA. The Tc values decreases linearly from 58.256 (free of PAA) to 55.168 °C (PAA in ILW) with increasing PAA concentrations in ILW. This indicates that the polymer chain entangles with the coexisting phases, thereby the polymer monomers strongly interact with neighbor solvent particles. At temperatures T close enough to Tc, the critical exponent (β) values were obtained from the measured n values of both the coexisting liquid phases and was found to increase from 0.332 to 0.379, when the PAA concentration changes from 0.5 to 1.5 mg cm−3. The obtained 3D Ising values are modified in the presence of PAA and obviously belong to the renormalized class. These values are higher than that of 0.326 ± 0.002 of pure ILW, which is compatible with the 3D Ising value β = 0.325. In addition, we have performed the fluorescence measurement for the determination of Tc for ILW and in the presence of PAA as an impurity. The observed increase in the fluorescence intensities with temperature predicts unambiguously the formation of the solvation structure at Tc for the critical mixture in presence of the polymer.

Synthesis and Characterization of Ni/Mg/Al Mixed Oxides Obtained by Co-precipitation

ABSTRACTNi/Mg/Al mixed oxides were obtained from hydrotalcite-like precursors by thermal decomposition at 400º, 600º and 800ºC using co-precipitation method at pH 7. The mixed oxides were characterized by X-ray diffraction (XRD), Scanning electron microscopy (SEM), and Energy-dispersive X-ray spectroscopy (EDS) techniques. XRD analysis revealed the formation of NixMg1-xO (x = 0 - 1), α-Al2O3 and traces of MgAl2O4 (NiAl2O4) phases. The diffraction peak positions for MgO or NiO oxides were shifted towards 2θ values higher than simulated for pure bulk oxides that can be attributed to the possible presence of lattice vacancies or surface compressive stress. The evaluated grain size by XRD technique was about 8 -10 nm. It was also detected the presence of microstrains that can be associated with the presence of extended defects in the grains. SEM observations showed that the particles of oxides are formed as agglomerates with the particle sizes of 50 nm up to 200 nm. EDS detected the presence of Mg2+, Ni2+, and Al3+ cations and oxygen in all particles independently on their size. The obtained results revealed the presence of mixture of Ni/Mg/Al oxides in each particle obtained. The oxides calcined at temperatures of 400º and 600ºC were unstable and under air storage they revert to the precursor. The incorporation of Ni2+ in Mg-Al mixed oxides leads to stability of the compounds calcined at 800ºC.

Multivariate Asset Return Prediction with Mixture Models

The use of mixture distributions for modeling asset returns has a long history in finance. New methods of demonstrating support for the presence of mixtures in the multivariate case are provided. The use of a two-component multivariate normal mixture distribution, coupled with shrinkage via a quasi-Bayesian prior, is motivated, and shown to be numerically simple and reliable to estimate, unlike the majority of multivariate GARCH models in existence. Equally important, it provides a clear improvement over use of GARCH models feasible for use with a large number of assets, such as CCC, DCC, and their extensions, with respect to out-of-sample density forecasting. A generalization to a mixture of multivariate Laplace distributions is motivated via univariate and multivariate analysis of the data, and an EM-algorithm is developed for its estimation in conjunction with a quasi-Bayesian prior. It is shown to deliver significantly better forecasts than the mixed normal, with fast and numerically reliable estimation. Crucially, the distribution theory required for portfolio theory and risk assessment is developed.

Nonadditive phenomena during polyaniline synthesis in the presence of mixtures of rigid-chain and flexible-chain polymer sulfoacids and their effect on properties of obtained interpolymer complexes

The matrix polymerization of aniline in the presence of mixtures of rigid-chain and flexible-chain polymer sulfoacids was investigated in the work. The optical, electric, and spectroelectrochemical properties of the forming interpolymer complexes of polyaniline, as well as their morphology, were studied. The dominating influence of rigid-chain polyacid on the process of formation of the interpolymer complexes of polyaniline even in the case of application of the mixture with the prevailing content of the flexible-chain polyacid was detected. The nonadditive dependence character of the viscosity of the mixtures of polyacid solutions, the duration of the induction period of aniline polymerization, and the optical absorbance and conductivity of the obtained complexes of polyaniline relative to polyacid ratios in the mixture was shown. The presence of the intermolecular interaction in the mixtures of polymer sulfoacids was shown via viscometry method, which may be the reason for the nonadditivity of the observed phenomena.

Simulation of cumene oxidation in the presence of a binary mixture of initiators

The oxidation of cumene in the presence of a mixture of two initiators, azobisisobutyronitrile and benzoyl peroxide, revealed the antagonistic effect of their action. This phenomenon was explained using mathematical simulation of the process by means of analyzing kinetic schemes. It was shown that the antagonistic effect is a result of formation of alkoxyl radicals at the stage of combination of cumene peroxyl radicals and their further participation in cross-termination reactions with initiator radicals. The temperature dependence of the initiators’ effect has been analyzed.

Establishment of anthocyanin-producing cell suspension cultures of Cleome rosea Vahl ex DC. (Capparaceae)

The effects of different levels of Murashige and Skoog (MS) basal medium, 2,4-dichlorophenoxyacetic acid (2,4-D), and sucrose on anthocyanin production and biomass accumulation of cell suspension cultures of Cleome rosea were investigated. Cultures were established in liquid MS medium containing 30 g l−1 sucrose and supplemented with 0.90 μM 2,4-D. Proliferating cell suspension cultures achieved the highest growth capacity, a fourfold increase in biomass accumulation, following subculture at the exponential growth phase, 14–18 days of culture. Moreover, the presence of 2,4-D was essential for anthocyanin production and biomass accumulation. On the other hand, increasing levels of sucrose above 30 g l−1 resulted in a drastic reduction in biomass accumulation. Anthocyanin production was highest in cell suspension cultures grown on half-strength MS medium (1/2 MS), 30 g l−1 sucrose, and 0.45 μM 2,4-D. These cell suspension cultures were mainly composed of small aggregates of spherical cells with similar morphology observed in anthocyanin-producing and non-producing cultures. Moreover, microscopic analysis of anthocyanin-producing cultures showed the presence of mixtures of non-pigmented, low-pigmented, and high-pigmented cells.

Effect of a combination of deoxynivalenol and nivalenol on lipopolisaccharide-induced nitric oxide production by mouse macrophages

Deoxynivalenol (DON) and nivalenol (NIV) are trichothecene mycotoxins produced by Fusarium fungi as secondary metabolites. Both compounds have the immunotoxic effects that the productions of inflammatory mediators by activated macrophages is disturbed. Co-contamination with DON and NIV can occur; however, the effects of simultaneous contamination are not well known. The present study investigated the combined effects of DON and NIV on nitric oxide (NO) production by mouse macrophages stimulated with lipopolisaccharide (LPS). The inhibitory effect of DON and NIV on NO release from activated macrophages has already been reported as an appropriate indicator of immunotoxic effect of the both compounds. LPS-induced NO production in macrophages was inhibited by both of these toxins individually in a dose-dependent manner, and toxin mixtures at the same concentration inhibited NO production in the same manner. In addition, there were no unique inhibitory effects on LPS-induced NO production in macrophages in the presence of mixtures of various molar ratios. These results suggest that the combined effects of DON and NIV can be predicted based on addition of each compound alone.

PHYSICAL MODEL ABOUT LASER IMPACT ON METALS AND ALLOYS

In this article we present our physical model for interaction of laser radiation with metals and alloys through structural changes, melting and vaporizing. We describe the interaction of laser radiation with materials, kinetic process of energy transmitting from free electrons to the crystal lattice and propagation of heat and the processing zone. We consider influence of optical and thermal properties over exploring process as they change with temperature and in the presence of mixtures.

Carbon quality rather than stoichiometry controls litter decomposition in a tropical rain forest

Summary 1. Ecological stoichiometry predicts important control of the relative abundance of the key elements carbon (C), nitrogen (N) and phosphorus (P) on trophic interactions. In a nutrient‐poor Amazonian lowland rain forest of French Guiana, we tested the hypothesis that decomposers exploit stoichiometrically diverse plant litter more efficiently, resulting in faster litter decomposition compared to litter with a uniform stoichiometry. 2. In a field experiment in the presence or absence of soil macrofauna, we measured litter mass loss, and N and P dynamics from all possible combinations of leaf litter from four common tree species which were distinctly separated along a C:N and along a N:P gradient. 3. Mean litter mass remaining after 204 days of field exposure varied between 25.2% and 71.3% among litter treatments. Fauna increased litter mass loss by 18%, N loss by 21% and P loss by 14%. Litter species richness had no effect on litter mass loss or nutrient dynamics. In contrast, litter mass and nutrient losses increased with increasing stoichiometric dissimilarity of litter mixtures in presence of fauna, suggesting faster decomposition of a stoichiometrically more heterogeneous litter. 4. However, the effect of stoichiometric dissimilarity was smaller than the strong C quality related litter composition effect and disappeared in the absence of fauna. Increasing proportions of litter that is relatively rich in accessible C compounds (non‐structural carbohydrates, phenolics) and relatively poor in recalcitrant C (condensed tannins, lignin), correlated best with litter mass loss irrespective of fauna presence. No correlation was found for any of the nutrient related litter quality parameters and decomposition. 5. Synthesis. Our results suggest that Amazonian decomposer communities studied here are primarily limited by energy, and only secondarily by litter stoichiometry. Tropical tree species might thus influence decomposers and detritivores by the production of litter of specific C quality with potentially important feedback effects on ecosystem nutrient dynamics and availability.

Simultaneous voltammetric determination of levodopa, carbidopa and benserazide in pharmaceuticals using multivariate calibration

An analytical methodology based on differential pulse voltammetry (DPV) on a glassy carbon electrode and the partial least-squares (PLS-1) algorithm for the simultaneous determination of levodopa, carbidopa and benserazide in pharmaceutical formulations was developed and validated. Some sources of bi-linearity deviation for electrochemical data are discussed and analyzed. The multivariate model was developed as a ternary calibration model and it was built and validated with an independent set of drug mixtures in presence of excipients, according with manufacturer specifications. The proposed method was applied to both the assay and the uniformity content of two commercial formulations containing mixtures of levodopa–carbidopa (10:1) and levodopa–benserazide (4:1). The results were satisfactory and statistically comparable to those obtained by applying the reference Pharmacopoeia method based on high performance liquid chromatography. In conclusion, the methodology proposed based on DPV data processed with the PLS-1 algorithm was able to quantify simultaneously levodopa, carbidopa and benserazide in its pharmaceuticals formulations using a ternary calibration model for these drugs in presence of excipients. Furthermore, the model appears to be successful even in the presence of slight potential shifts in the processed data, which have been taken into account by the flexible chemometric PLS-1 approach.

Effect of matrix domination in PANI interpolymer complexes with polyamidosulfonic acids

Various polyaniline (PANI) interpolymer complexes with polyacids in the form of molecular solutions were synthesized by chemical oxidative polymerization of aniline in the presence of water-soluble poly-(2-acrylamido-2-methyl-1-propanesulfonic acid) (flexible backbone), poly-p,p′-(2,2′-disulfoacid)-diphenylene-terephthalamide (t-PASA, rigid backbone), and their mixtures in different ratios. The complexes were characterized by UV-Vis-near infrared spectroscopy in solutions; also, the films’ drop-casts from these solutions were investigated by cyclic voltammetry, spectroelectrochemical, direct current (DC) conductivity, and atomic force microscopy (AFM) measurements. It was shown that the nature of polyacid affects the shape of spectra and the dynamics of their changes. The character of spectral changes during the matrix synthesis of PANI in the presence of mixtures of the rigid-chain and flexible-chain matrixes and the study of spectral properties of the obtained PANI solutions demonstrates the existence of the rigid-matrix domination effect in the process of formation of PANI interpolymer complexes. Spectral properties of the obtained PANI complexes with the mixtures of flexible-chain and rigid-chain polyacids of different ratios (3:1, 1:1, 1:3, and 1:6) are very similar to those ones for the complex with rigid-chain t-PASA. At the same time, there is a correlation between the electrical conductivity and morphology of the films of PANI complexes and their composition, the conductivity passing through a minimum for the complexes with the polyacid mixtures (6:1, 3:1, and 1:1).

Similarity, independence, or interaction for binary mixture effects of nerve toxicants for the nematode Caenorhabditis elegans

Intensive agriculture can require the simultaneous use of more than one pesticide, resulting in the presence of mixtures in soils and waters. To assess mixture effects, concentration addition (CA) for similar acting chemicals and independent action (IA) for dissimilar acting chemicals are the most frequently used models. While the mechanistic basis for the selection of CA and IA for a given mixture appears appealing (similar vs dissimilar action), it has not yet been established how similar chemicals need to be in their effect before CA should be viewed as the most appropriate model. Here this is investigated in studies of the toxicity of binary mixtures of five different pesticides from three classes that have the same putative mode of action (neuroexcitation) but different molecular mechanisms in binary mixture tests with the nematode Caenorhabditis elegans. Effects of exposure on nematode survival were limited at the concentrations tested. Data analysis, therefore, focused on reproductive toxicity. Both CA and IA were found to be valid models for prediction of the toxicity of the 10 mixtures, although for seven CA provided a mathematically better fit. Both models could describe the toxicity for four mixtures; however, evidence for interaction was found in the remaining six cases. Where interactions occurred, these could be explained by information on the potential mechanisms of compound toxicokinetics-particularly when mixtures comprised a metabolically activated and a metabolically deactivated chemical and/or cases where the relative potencies of the two tested chemicals differed greatly. It is concluded, therefore, that detailed analysis of toxicokinetics and toxicodynamics can aid further understanding of interactions in mixtures.

Spectrofluorimetric determination of carvedilol in dosage form and spiked human plasma through derivatization with 1-dimethylaminonaphthalene-5-sulphonyl chloride

A sensitive, simple and selective spectrofluorimetric method was developed for the determination of carvedilol (CA) in pharmaceutical formulation and a biological fluid. The method is based on the reaction between the drug and 1-dimethylaminonaphthalene- 5-sulphonyl chloride (dansyl chloride) in the presence of mixture (acetone:0.5 M sodium carbonate, 3:2) at pH 10 to yield a highly fluorescent derivative that is measured at 445 nm after excitation at 350 nm. Different experimental parameters affecting the development and stability of the reaction product were carefully studied and optimized. The fluorescence concentration plot was rectilinear over the range of 5.0-80.0 ng ml-1 with a lower detection limit (LOD) of 1.90 ng ml-1 and the limit of quantitation (LOQ) of 5.15 ng ml-1. Quantum yield, formation constant (K) and free energy change (?G) values were calculated. The proposed method was successfully applied to the analysis of commercial tablets. The results obtained were in good agreement with those obtained using the official titrimetric method [1,2]. Furthermore, the method was applied for the determination of CA in spiked human plasma, the mean % recovery (n = 5) is 97.82?0.373. A proposal of the reaction pathway was presented.

Analysis of severe feather pecking behavior in a high feather pecking selection line

Even though feather pecking (FP) in laying hens has been extensively studied, a good solution to prevent chickens from this behavior under commercial circumstances has not been found. Selection against FP behavior is possible, but for a more effective selection across different populations, it is necessary to characterize the genetic mechanism associated with this behavior. In this study, we use a high FP selection line, which has been selected for 8 generations. We present evidence of the presence of a major dominant allele affecting the FP behavior by using an argument based on the presence of mixture in the distribution of the observed FP and by studying the evolution of the proportion of very high FP along the sequence of 8 generations. This hypothesis is further supported by the fact that the gene transcription profile of the birds performing high FP differs from the profile of the other birds performing FP (456 genes differentially expressed from a total of 14,077 investigated genes).

Peculiarities of polyaniline matrix synthesis in the presence of mixtures of different types of matrices and investigation of properties of formed interpolymer complexes

In the present work, the existence of a matrix domination effect in the formation process in polyaniline interpolymer complex solutions under aniline oxidation in the presence of rigid and flexible poly(amidosulfonic acid)s was demonstrated for the first time.

Direct Visualization of the Lateral Structure of Porcine Brain Cerebrosides/POPC Mixtures in Presence and Absence of Cholesterol

We studied the thermal behavior of membranes composed of mixtures of natural cerebrosides (from porcine brain) and 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) with and without cholesterol, using differential scanning calorimetry, Fourier transform infrared spectroscopy, and confocal/multiphoton fluorescence microscopy. The POPC/cerebroside mixture display solid ordered/liquid disordered phase coexistence in a broad range of compositions and temperatures in agreement with previous results reported for POPC/(bovine brain)cerebrosides. The observed phase coexistence scenario consists of elongated, micrometer-sized cerebroside-rich solid ordered domains that span the bilayer, embedded in a POPC-rich liquid disordered phase. The data obtained from differential scanning calorimetry and Fourier transform infrared spectroscopy was in line with that obtained in the microscopy experiments for the binary mixture, except at very high cerebroside molar fractions (0.8–0.9) were some differences are observed. Cholesterol incorporation exerts strong changes on the lateral organization of POPC/porcine brain cerebroside membranes. At intermediate cholesterol concentrations (10–25 mol %) the solid ordered/liquid disordered phase coexistence scenario gradually transform to a solid ordered/liquid ordered one. Above 25 mol % of cholesterol two distinct regions with liquid ordered phase character are visualized in the membrane until a single liquid ordered phase forms at 40 mol % cholesterol. The observed cholesterol effect largely differs from that reported for POPC/porcine brain ceramide, reflecting the impact of the sphingolipids polar headgroup on the membrane lateral organization.

DNA Condensation into Inverted Hexagonal Phase in Aqueous Dispersion of Poly(Ethylene)-Functionalized Dioleoylphosphatidylethanolamine and Metal Cations

We report the x-ray diffraction study of the structure and phase behavior of mixtures of dioleoylphosphatidylethanolamine (DOPE) and poly(ethyleneglycol)-functionalized DOPE (DOPE:PEG(350)) in aqueous dispersions of DNA and bivalent metal cations. Characterization of the phase behaviour of DOPE/DOPE:PEG(350) mixtures in presence of metal cations without DNA is also performed: over a definite amount of the PEG-lipid component, a phase transition from the inverted hexagonal phase H II to the bicontinuous inverted cubic phase, with space group Pn3m is induced. Moreover, it is shown that at low concentration of PEG-lipid component, the inverted hexagonal phase is found on adding DNA to the aqueous dispersions of DOPE/DOPE:PEG and metal cations. This structure consists of cylindrical DNA strands coated by neutral lipid monolayers and arranged on a two-dimensional hexagonal lattice. The results here shown represent the first experimental evidence of a self-assembled formation of an inverted hexagonal complex structure in aqueous dispersions of DNA, metal cations and liposomes made of mixtures of pure and pegylated lipids. The surface functionalization with the PEG-lipid and the evidence of the formation of the complexes are important results in the perspective of the development of appropriate vectors for drug delivery and gene transfection.

Structural studies of ionic liquid-modified microemulsions

This work is focused on the influence of an ionic liquid (IL), i.e. ethyl-methylimidazolium hexylsulfate, on the spontaneous formation of microemulsions with ionic surfactants. The influence of the ionic liquid on structure formation in the optically clear phase region in water/toluene/pentanol mixtures in presence of the cationic surfactant CTAB was studied in more detail. The results show a significant increase of the transparent phase region by adding the ionic liquid. Conductometric investigations demonstrate that adding the ionic liquid can drastically reduce the droplet–droplet interactions in the L 2 phase. 1H nuclear magnetic resonance ( 1H NMR) diffusion coefficient measurements in combination with dynamic light scattering measurements clearly show that inverse microemulsion droplets still exist, but the droplet size is decreased to 2 nm. A more detailed characterisation of the isotropic phase channel by means of conductivity measurements, dynamic light scattering (DLS), 1H NMR and cryo-scanning electron microscopy (SEM), allows the identification of a bicontinuous sponge phase between the L 1 and L 2 phase. When the poly(ethyleneimine) is added, the isotropic phase range is reduced drastically, but the inverse microemulsion range still exists.